Nucleon structure studies with CLAS: current status and...

Nucleon structure studies with CLAS: current status

and prospects after 12 GeV Upgrade

V.I.Mokeev

Collaboration between SINP at MSU and Hall B at

Jefferson Lab

Nucleon structure studies with CLAS

• Parton distributions, twist decomposition from the

studies of inclusive polarized and unpolarized

structure functions

• Transversity, quark orbital angular momentum from

semi- inclusive meson electroproduction

• GPD studies : 3-dimensional image of nucleon, full

access to quark total angular momentum, mass and

‘pressure’ distributions in the ground nucleon state

• The studies of excited nucleon state (N*) structure

through the data on transition N-N* form factors

Access to non-perturbative strong interaction

mechanisms, that are responsible for baryon

formation from quarks and gluons and their relation to

QCD.

Dressed quark properties and transition from non-

perturbative to perturbative regimes of strong

interactions

• ~few MeV current quark mass is approached at

asymptotically high momentum p running over quark

• sharp mass evolution at p<2.0 GeV reflects transition

between non-perturbative/perturbative regime of strong

interaction

•mass dependence is directly related to QCD b-

function

•>98% of nucleon mass comes from dynamical

dressing of current quarks

The studies of the ground and excited nucleon state structure allow

us to access properties and interactions of dressed quarks at

various distance scales

Key part in the studies of quark confinement in baryons!

Emax

~ 6 GeV

Imax ~ 200 mA

Duty Factor ~ 100%

sE/E ~ 2.5 10-5

Beam P ~ 80%E

g(tagged) ~ 0.8- 5.5

GeV

CLAS

Ускоритель электронов непрерывного действия в Jefferson Lab –

CEBAF

CEBAF Large Acceptance Spectrometer

Liquid D2 (H2)target +

start counter; e minitorus

Drift chambers

argon/CO2 gas, 35,000 cells

Electromagnetic calorimeters

Lead/scintillator, 1296 PMTs

Torus magnet

6 superconducting coils

Gas Cherenkov counters

e/p separation, 216 PMTs

Time-of-flight counters

plastic scintillators, 684 PMTs

Large angle calorimeters

Lead/scintillator, 512 PMTs

12 GeV

Enhance equipment

in existing halls

Add new hall

CHL-2

CLAS12

Central

Detector

Forward

Detector

CLAS12

2m

3/25/09 7

CLAS12 – Central Detector SVT, CTOF

Charged particle

tracking in 5T field

ΔT < 60psec in for

particle id

Moller electron

shield

Polarized target

operation ΔB/B<10-4

3/25/09 8

World data on polarized structure

function g1p(x,Q2)

CLAS provides a large

body of precise g1 data in

the DIS and transition

regions that can be used

to improve knowledge of

twist-2 PDFs.

Phys. Rev.C75:035203, 2007

Phys. Lett. B 641, 11 (2006)

Spin structure functions – Hall B

²),(

²),(²),(

2

2

1Qxqe

QxqeQxA

ii

iiLO

LO extraction of quark polarization

Effect of these data on NLO analysis

High discriminating power of the different models

High sensitivity to G even if probes the valence region

Spin structure functions – Hall B

²),(²),( 21

' QxAQxADAll - 30 days on NH3 (P=0.8)

- 50 days on ND3 (P=0.4)

- L = 1035 /cm²/s @ 11 GeV W > 2 GeV; Q2 > 1 GeV²

Proton Deuteron

SIDIS and TMDs

Nucleon structure at 12 GeV GHP09, 04/29/2009 S.Procureur

- Semi-inclusive DIS allows separation of different quark contributions

- Also gives the transverse momentum distribution of quarks

- Spin-orbit correlations through azimuthal distributions

requires non zero OAM

Mesure single & double spin asymmetries on pions

Large acceptance needed (CLAS12)

)( TkPS

SIDIS and TMDs


- 30 days on NH3 (P=0.8)

- 50 days on ND3 (P=0.4)

- L = 1035 /cm²/s @ 11 GeV

qq

qq

LqUL zHxxheA,

11

22sin )()(

)()(4

)()(4

xdxu

xdxuA

VV

VVp

-

-

- -pp

)()(

)()(

xdxu

xdxuA

VV

VVd

- -pp

Introduction to GPDs


),,(~

,,~

, txEEHH

Deconvolution

needed

Introduction to GPDs

Longitudinal momentum

distribution

(momentum space)

Form factors Parton distributions

Transverse charge

distribution

(coordinate space)

Correlation between

longitudinal momentum

& transverse spatial distributions

GPD

Physical content of GPD E & H

M2(t) : Mass distribution inside the nucleonJ (t) : Angular momentum distributiond1(t) : Forces and pressure distribution

Nucleon matrix element of the Energy-Momentum Tensor of QCD contains three scalar form factors (R. Pagels, 1965) and can be written as (X. Ji, 1997):

GPDs are related to these form factors through 2nd moments

To determine J(t) we need to measure the x and t dependence of GPDs.To separate M2(t) and d1(t) we need measurements at small and large ξ(xB).

DVCS and GPDs

...),,(),,(

1

1

--

-

txGPDidxx

txGPDP p

Experimentally: DVCS cannot be distinguished with BH process

requires high Q², with t<<Q²

- Deep Virtual Compton Scattering is the most suitable process to probe GPDs

- Factorization theorem states that the « handbag » diagram is the only

contribution to the DVCS amplitude in the suitable asymptotic limit

...),,(

1

1

-

-

dxix

txGPDT DVCS

DVCS

BH

p p

e ed4s

dQ2dxBdtd~ |TDVCS + TBH|2

TBH calculable from

elastic form factorsInterference gives direct access to DVCS amplitude

Extraction of GPDs

A =s

2s

s - s-

s s- =

sUT ~ sin{k(F2H – F1E) + ….. }

Different combinations of GPDs can be accessed with polarized beam or target

• Polarized beam, unpolarized target (BSA):

• Unpolarized beam, longitudinal target (TSA):

• Unpolarized beam, transverse target (TSA):

sUL ~ sin{F1H+ξ(F1+F2)(H +ξ/(1+ξ)E) -.. }~

sLU ~ sin{F1H + ξ(F1+F2)H +kF2E}~

H (H,E)~

H (H,E)~

H,E

Kinematically suppressed



DVCS – Hall B


- 80 days of polarized beam on LH2 target (BSA)

- L = 1035 /cm²/s @ 11 GeV

Extraction of H

A =s

2s

s - s-

s s- =

sLU ~ sinF1H + …

Ground state and P11(1440) electrocouplings & quark model

expectations

Ground p state P11(1440)

S.Capstick

light cone (LC)

model

B.Metsch

Bethe-Salpeter

model

I.Aznauryan

LC model

M.Giannini/

E.Santopinto

hyper-centric

CQM

3q core3q core +??

The studies of both the ground and excited nucleon structure are needed in order to

understand how non-perturbative strong interactions create nucleons and how they

emerge from QCD

The studies of excited nucleon state

structure in meson electroproduction with

CLAS

OEPVAYa Seminar (led by B.S.Ishkhanov) June

23, 4pm, Bld #19, room #215

22

Nucleon Resonance Studies with CLAS12

D. Arndt4, H. Avakian6, I. Aznauryan11, A. Biselli3, W.J. Briscoe4, V. Burkert6,

V.V. Chesnokov7, P.L. Cole5, D.S. Dale5, C. Djalali10, L. Elouadrhiri6, G.V. Fedotov7,

T.A. Forest5, E.N. Golovach7, R.W. Gothe*10, Y. Ilieva10, B.S. Ishkhanov7,

E.L. Isupov7, K. Joo9, T.-S.H. Lee1,2, V. Mokeev*6, M. Paris4, K. Park10,

N.V. Shvedunov7, G. Stancari5, M. Stancari5, S. Stepanyan6, P. Stoler8,

I. Strakovsky4, S. Strauch10, D. Tedeschi10, M. Ungaro9, R. Workman4,

and the CLAS Collaboration

JLab PAC 34, January 26-30, 2009

Approved for 60 days beamtime

Argonne National Laboratory (IL,USA)1, Excited Baryon Analysis Center (VA,USA)2,Fairfield University (CT, USA)3, George Washington University (DC, USA)4,

Idaho State University (ID, USA)5, Jefferson Lab (VA, USA)6,Moscow State University (Russia)7, Rensselaer Polytechnic Institute (NY, USA)8,University of Connecticut (CT, USA)9, University of South Carolina (SC, USA)10,

and Yerevan Physics Institute (Armenia) 11

SpokespersonContact Person*

Projections for N* Transitions

For the foreseeable future, CLAS12 will be the only facility worldwide, which will be able to access the N* electrocouplings in the Q2 regime of 5 GeV2 to 10 GeV2, where the quark degrees of freedom are expected to dominate. Our experimental proposal “Nucleon Resonance Studies with CLAS12” was approved by PAC34 for the full 60-day beamtime request.

http://www.physics.sc.edu/~gothe/research/pub/nstar12-12-08.pdf.

CLAS published

CLAS PRL subm.

CLAS12projected

CLAS published

CLAS preliminay

CLAS12 projected

CLAS12

Conclusions and outlookThe 6 GeV Program provided:

•comprehensive data on various inclusive structure functions , their

moments and improve considerably our knowledge on parton

distributions

•extensive information on N-N* transition amplitudes for several excited

proton states at Q2<5.0 GeV2 for the first time determined with CLAS

•first information on various SIDIS polarization observables neded to

access parton transverse distributions and quark orbital momentum in

nucleons

•first data on DVCS asymmetries allowing us to access GPD structure

functions

After 12 GeV Upgrade CLAS12 will be only facility foreseen worldwide, that

will be capable to study nucleon structure at still fully unexplored area of

5.0<Q2<14 GeV2, where quark degrees of freedom are expected to dominate.

Nucleon structure studies in this area will allow us to understand dressed quark

interactions, that are responsible for nucleon formation and their emergence

from QCD

Backup

Overview of Technical Performance Requirements

Hall D Hall B Hall C Hall A

excellent hermeticity

luminosity

10 x 1034

energy reach installation space

polarized photons hermeticity precision

E~8.5-9 GeV 11 GeV beamline

108 photons/s target flexibility

good momentum/angle resolution excellent momentum resolution

high multiplicity reconstruction luminosity up to 1038

particle ID

CD-0 Mission Need MAR-2004 (A)

CD-1 Preliminary Baseline Range FEB-2006 (A)

CD-2 Performance Baseline NOV-2007 (A)

CD-3 Start of Construction SEP-2008 (A)

CD-4A Accelerator Project Completion and Start of

OperationsDEC-2014

CD-4B Experimental Equipment Project Completion and

Start of OperationsJUN-2015

(A) = Actual Approval Date

Now split in two to ease transition into operations phase


DOE critical decision schedule

E12-07-109 (Hall A)E12-07-104 (Hall B)PR12-09-001 (Hall C)


Measurements of Form Factors

Deeply Virtual Exclusive Processes -Kinematics Coverage of the 12 GeV Upgrade

H1, ZEUS

11 GeV

H1, ZEUSStudy of high xB domain requires high luminosity

0.7

HERMES

COMPASS

The 12 GeV Upgrade is well matched to GPD studies in the valence quark regime.

Cross section

DVCS

asymmetry

DVCS and GPDs

Nucleon structure studies with CLAS: current status and...

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